In digital photographing, an image of a field of view is drawn on a camera sensor that forms a digital image. For concentrating light on the camera sensor, an objective is used as known from camera systems. An impression of depth in the picture can be obtained by producing a restricted accurate field of depth. Objects closer or farther than so-called focal plane appear increasingly blurred, which enables highlighting desired objects. Auto-focus enables a camera to maintain selected objects of interest in focus when the distance between the camera and the objects changes or if the focal length of the objective is changed by zooming in or out.
For autofocus, the camera needs to know which parts of the image should be focused. To this end, the auto-focus may employ face detection or other algorithms to find likely interesting targets. At simplest, the user identifies the target point by aiming a single focusing point towards the desired object e.g. by pressing a trigger button halfway down to lock the focus and then turns the camera to frame the image in some other way, if necessary. In some enhanced cameras, the auto-focus is configured to track the object of interest and maintain focusing on it even when the object travels. Such tracking auto-focus, also known as AI servo or continuous focusing, is useful when taking pictures of flying birds, for instance.